In one type of electrically controlled light emitting device, organic material is placed between a layer of conductive material that can inject electrons and a layer of conductive material that can inject holes. When a voltage of proper polarity is applied between the outer layers of conductive material, electrons from one layer combine with holes from the other so as to release energy as light that is, to produce electroluminescence (EL). These devices are referred to as organic light emitting devices, OLED's.
OLED's have been constructed from polymers so as to have a highly advantageous flexibility that enables them to be used for light weight, portable, roll-up displays or to be used for conformable displays which can be readily attached to windows, windshields or instrument panels that may have curved surfaces; “The Plastic LED: A Flexible Light-Emitting Device Using a Polyaniline Transparent Electrode” by G. Gustafsson et al in “Synthetic Metals”, 55-57 4123-4227 (1993). Even though there is a widespread application of vacuum-deposited, small-molecule-based heterostructural OLED's, which have been constructed on inflexible glass substrates and use ITO as the hole emitting layer, the devices of Gustafsson were fabricated using a polymer, that is, soluble semiconducting polymer poly(2-methoxy,5-(2′-ethyl-hexoxy)-1,4-phenylene-vinylene) (MEH-PPV) as the emissive layer, since the mechanical properties of polymers were deemed to be unique with respect to making such devices.
It would be desirable if flexible OLED's could be fabricated having improved electroluminescent properties as well as the advantage of being readily fabricated using the vacuum deposition techniques typically used for preparing OLED's